The enormous wels catfish is rapidly expanding in German waters. The fish can grow up to 10 feet long and weigh over 300 pounds, making recreational fishermen excited about the prospects of catching one. While biologists aren’t yet calling the fish pests, they are puzzled by the boom … //

… Fourteen Tons of Catch in a Year:

Regardless, the meager figures that do exist document an impressive development. In the 1980s there were few reports of wels catfish catches. In 1996 there were 656 kilograms registered, a figure that jumped to 1,282 kilos the next year. The most recent figures come from 2010, when fishermen caught more than 14 tons of the fish from the Rhine.

“The wels catfish never played much of a role in our waters,” Staas says. “That has changed.” He suspects human activity may be behind the boom, in the form of uncontrolled releases. Manuel Lankau, biologist with the Westphalia Fishermen’s Association, agrees. “It’s highly possible that the wels catfish has spread because of fish stocking policies, and that in recent years the diverse populations have coalesced.”

The warmth-loving fish is finding an ideal habitat in the Rhine, where temperatures are steadily rising. “The introduction of power plants on the river has heated things up,” Staas says. Global warming has also played a role in the rising temperatures.

The wels catfish lays 25,000 eggs in one clutch. After three years, the young fish are ready to breed, and after another three years they typically grow to be a meter long. While the fish naturally spawns only once every 10 years, the summer temperatures in the Rhine apparently increase the capacity to breed each year. Still Lankau, the biologist, says he wouldn’t call the fish a menace. “The wels catfish will not deprive itself of its own basic food source by eating up all the other fish,” he says.